1. Field of the Invention
This invention pertains generally to excitation control systems for rotating electrical apparatus and, more particularly, to such systems which provide excitation voltage to a generator.
2. Background Information
Three-phase rectifier circuits are commonly employed to convert AC signals to DC signals. These circuits often use SCRs disposed in bridge segments, with typically one SCR for each polarity of each AC phase. Typically, a bridge firing control circuit controls the firing point for each rectifier in each AC cycle.
SCR bridges are commonly employed in an excitation control system to provide field excitation for a rotating electrical apparatus (e.g., large synchronous generators and motors, utility synchronous generators and motors, industrial synchronous generators and motors, synchronous generators and motors for naval or other shipping applications, synchronous generators and motors for oil well drilling rigs).
For example, when the generator is on-line, generator field excitation is provided thereto. Whenever the generator is on-line and providing power to a load, the generator circuit breaker is closed. An auxiliary contact of the generator circuit breaker is employed to indicate the closed or open status of the breaker and, thus, the on-line or off-line status, respectively, of the generator. In turn, generator tripping logic or protection logic employs this closed or open status to adjust trip thresholds in the trip logic or to adjust limiters in the protection logic.
If the auxiliary contact erroneously indicates an off-line status for an on-line generator, then the trip or protection logic may cause a reduction of excitation to the online generator and, thus, cause it to improperly enter the off-line state, thereby interrupting power to the load and adversely impacting the availability of the generator.
Accordingly, there is room for improvement.